This invention relates to instrumentation and techniques for checking the performance of internal combustion engines.
Although power output, customarily measured in terms of brake horsepower, is a parameter of primary importance in evaluating engine performance, no really convenient means for testing this aspect of engine operation in the field is presently available. Engine stand dynamometers are utilized for this purpose during development of an engine and in the factory but are complex and costly installations, requiring highly skilled operators. Power output evaluation with an engine stand dynamometer is not usually a practical procedure for testing engines at a work installation whether stationary or on a vehicle. Chassis dynamometers, commonly used for checking installed vehicle engines, measure wheel horsepower by applying a controlled braking force to the traction wheels of the immobilized vehicle. Chassis dynamometer measurements also require complex apparatus and the results are of limited accuracy as the critical measurement is not taken at the engine itself but is subject to variables introduced within the vehicle drive train.
While some other forms of power measurement means have been developed for checking engine power performance in a work environment, these have not proved to be fully satisfactory for various reasons such as the need for cumbersome equipment or inherent inaccuracies.
In practice, the lack of an economical and convenient means for checking engine power output in the field has created substantial servicing complications for manufacturers. Virtually any specific engine design is exhaustively evaluated in all respects prior to manufacture to establish, among other parameters, a rated power output at any of various speeds within the operating range. Subsequently, engines coming off the production line are tested and rejected unless performance conforms to the established values within small limits which may typically be plus or minus three percent in the case of rated power output. Once the engine has been installed in a working environment, the user may sometimes empirically come to the conclusion that less than the rated power output is being delivered. Owing to the lack of a convenient means for checking performance in this respect, it has been a common practice to attempt to establish the fact of satisfactory performance by systematically replacing various engine components which might possibly be defective or be malfunctioning. In instances where this inefficient procedure does not produce any obvious increase in power output, the question remains essentially unanswered and may be a source of continuing dissatisfaction to the user of the engine.
Accordingly a need exists for a practical technique and instrumentation for quickly, reliably and economically checking the power output of engines including engines situated in working environments such as a moving vehicle.